Add a new `compare_bytes` intrinsic instead of calling `memcmp` directly

6 files changed, 158 insertions, 2 deletions

diff --git a/tests/codegen/intrinsics/compare_bytes.rs b/tests/codegen/intrinsics/compare_bytes.rs
new file mode 100644
index 00000000000..e69224d818c
--- /dev/null
+++ b/tests/codegen/intrinsics/compare_bytes.rs
@@ -0,0 +1,34 @@
+// revisions: INT32 INT16
+// compile-flags: -O
+// [INT32] ignore-16bit
+// [INT16] only-16bit
+
+#![crate_type = "lib"]
+#![feature(core_intrinsics)]
+
+use std::intrinsics::compare_bytes;
+
+#[no_mangle]
+// CHECK-LABEL: @bytes_cmp(
+pub unsafe fn bytes_cmp(a: *const u8, b: *const u8, n: usize) -> i32 {
+    // INT32: %[[TEMP:.+]] = tail call i32 @memcmp(ptr %a, ptr %b, {{i32|i64}} %n)
+    // INT32-NOT: sext
+    // INT32: ret i32 %[[TEMP]]
+
+    // INT16: %[[TEMP1:.+]] = tail call i16 @memcmp(ptr %a, ptr %b, i16 %n)
+    // INT16: %[[TEMP2:.+]] = sext i16 %[[TEMP1]] to i32
+    // INT16: ret i32 %[[TEMP2]]
+    compare_bytes(a, b, n)
+}
+
+// Ensure that, even though there's an `sext` emitted by the intrinsic,
+// that doesn't end up pessiming checks against zero.
+#[no_mangle]
+// CHECK-LABEL: @bytes_eq(
+pub unsafe fn bytes_eq(a: *const u8, b: *const u8, n: usize) -> bool {
+    // CHECK: call {{.+}} @{{bcmp|memcmp}}(ptr %a, ptr %b, {{i16|i32|i64}} %n)
+    // CHECK-NOT: sext
+    // INT32: icmp eq i32
+    // INT16: icmp eq i16
+    compare_bytes(a, b, n) == 0_i32
+}
diff --git a/tests/ui/consts/const-compare-bytes-ub.rs b/tests/ui/consts/const-compare-bytes-ub.rs
new file mode 100644
index 00000000000..2b4062fd22b
--- /dev/null
+++ b/tests/ui/consts/const-compare-bytes-ub.rs
@@ -0,0 +1,41 @@
+// check-fail
+
+#![feature(core_intrinsics)]
+#![feature(const_intrinsic_compare_bytes)]
+use std::intrinsics::compare_bytes;
+use std::mem::MaybeUninit;
+
+fn main() {
+    const LHS_NULL: i32 = unsafe {
+        compare_bytes(0 as *const u8, 2 as *const u8, 0)
+        //~^ ERROR evaluation of constant value failed
+    };
+    const RHS_NULL: i32 = unsafe {
+        compare_bytes(1 as *const u8, 0 as *const u8, 0)
+        //~^ ERROR evaluation of constant value failed
+    };
+    const DANGLING_PTR_NON_ZERO_LENGTH: i32 = unsafe {
+        compare_bytes(1 as *const u8, 2 as *const u8, 1)
+        //~^ ERROR evaluation of constant value failed
+    };
+    const LHS_OUT_OF_BOUNDS: i32 = unsafe {
+        compare_bytes([1, 2, 3].as_ptr(), [1, 2, 3, 4].as_ptr(), 4)
+        //~^ ERROR evaluation of constant value failed
+    };
+    const RHS_OUT_OF_BOUNDS: i32 = unsafe {
+        compare_bytes([1, 2, 3, 4].as_ptr(), [1, 2, 3].as_ptr(), 4)
+        //~^ ERROR evaluation of constant value failed
+    };
+    const LHS_UNINIT: i32 = unsafe {
+        compare_bytes(MaybeUninit::uninit().as_ptr(), [1].as_ptr(), 1)
+        //~^ ERROR evaluation of constant value failed
+    };
+    const RHS_UNINIT: i32 = unsafe {
+        compare_bytes([1].as_ptr(), MaybeUninit::uninit().as_ptr(), 1)
+        //~^ ERROR evaluation of constant value failed
+    };
+    const WITH_PROVENANCE: i32 = unsafe {
+        compare_bytes([&1].as_ptr().cast(), [&2].as_ptr().cast(), std::mem::size_of::<usize>())
+        //~^ ERROR evaluation of constant value failed
+    };
+}
diff --git a/tests/ui/consts/const-compare-bytes-ub.stderr b/tests/ui/consts/const-compare-bytes-ub.stderr
new file mode 100644
index 00000000000..54fafded07b
--- /dev/null
+++ b/tests/ui/consts/const-compare-bytes-ub.stderr
@@ -0,0 +1,54 @@
+error[E0080]: evaluation of constant value failed
+  --> $DIR/const-compare-bytes-ub.rs:10:9
+   |
+LL |         compare_bytes(0 as *const u8, 2 as *const u8, 0)
+   |         ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ memory access failed: null pointer is a dangling pointer (it has no provenance)
+
+error[E0080]: evaluation of constant value failed
+  --> $DIR/const-compare-bytes-ub.rs:14:9
+   |
+LL |         compare_bytes(1 as *const u8, 0 as *const u8, 0)
+   |         ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ memory access failed: null pointer is a dangling pointer (it has no provenance)
+
+error[E0080]: evaluation of constant value failed
+  --> $DIR/const-compare-bytes-ub.rs:18:9
+   |
+LL |         compare_bytes(1 as *const u8, 2 as *const u8, 1)
+   |         ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ memory access failed: 0x1[noalloc] is a dangling pointer (it has no provenance)
+
+error[E0080]: evaluation of constant value failed
+  --> $DIR/const-compare-bytes-ub.rs:22:9
+   |
+LL |         compare_bytes([1, 2, 3].as_ptr(), [1, 2, 3, 4].as_ptr(), 4)
+   |         ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ memory access failed: alloc6 has size 3, so pointer to 4 bytes starting at offset 0 is out-of-bounds
+
+error[E0080]: evaluation of constant value failed
+  --> $DIR/const-compare-bytes-ub.rs:26:9
+   |
+LL |         compare_bytes([1, 2, 3, 4].as_ptr(), [1, 2, 3].as_ptr(), 4)
+   |         ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ memory access failed: alloc13 has size 3, so pointer to 4 bytes starting at offset 0 is out-of-bounds
+
+error[E0080]: evaluation of constant value failed
+  --> $DIR/const-compare-bytes-ub.rs:30:9
+   |
+LL |         compare_bytes(MaybeUninit::uninit().as_ptr(), [1].as_ptr(), 1)
+   |         ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ reading memory at alloc17[0x0..0x1], but memory is uninitialized at [0x0..0x1], and this operation requires initialized memory
+
+error[E0080]: evaluation of constant value failed
+  --> $DIR/const-compare-bytes-ub.rs:34:9
+   |
+LL |         compare_bytes([1].as_ptr(), MaybeUninit::uninit().as_ptr(), 1)
+   |         ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ reading memory at alloc25[0x0..0x1], but memory is uninitialized at [0x0..0x1], and this operation requires initialized memory
+
+error[E0080]: evaluation of constant value failed
+  --> $DIR/const-compare-bytes-ub.rs:38:9
+   |
+LL |         compare_bytes([&1].as_ptr().cast(), [&2].as_ptr().cast(), std::mem::size_of::<usize>())
+   |         ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ unable to turn pointer into integer
+   |
+   = help: this code performed an operation that depends on the underlying bytes representing a pointer
+   = help: the absolute address of a pointer is not known at compile-time, so such operations are not supported
+
+error: aborting due to 8 previous errors
+
+For more information about this error, try `rustc --explain E0080`.
diff --git a/tests/ui/consts/const-compare-bytes.rs b/tests/ui/consts/const-compare-bytes.rs
new file mode 100644
index 00000000000..74e29f81386
--- /dev/null
+++ b/tests/ui/consts/const-compare-bytes.rs
@@ -0,0 +1,27 @@
+// run-pass
+
+#![feature(core_intrinsics)]
+#![feature(const_intrinsic_compare_bytes)]
+use std::intrinsics::compare_bytes;
+
+fn main() {
+    const A: i32 = unsafe {
+        compare_bytes(1 as *const u8, 2 as *const u8, 0)
+    };
+    assert_eq!(A, 0);
+
+    const B: i32 = unsafe {
+        compare_bytes([1, 2].as_ptr(), [1, 3].as_ptr(), 1)
+    };
+    assert_eq!(B, 0);
+
+    const C: i32 = unsafe {
+        compare_bytes([1, 2, 9].as_ptr(), [1, 3, 8].as_ptr(), 2)
+    };
+    assert!(C < 0);
+
+    const D: i32 = unsafe {
+        compare_bytes([1, 3, 8].as_ptr(), [1, 2, 9].as_ptr(), 2)
+    };
+    assert!(D > 0);
+}
diff --git a/tests/ui/proc-macro/meta-macro-hygiene.stdout b/tests/ui/proc-macro/meta-macro-hygiene.stdout
index e476a8024fd..ac65ba07512 100644
--- a/tests/ui/proc-macro/meta-macro-hygiene.stdout
+++ b/tests/ui/proc-macro/meta-macro-hygiene.stdout
@@ -18,7 +18,7 @@ Respanned: TokenStream [Ident { ident: "$crate", span: $DIR/auxiliary/make-macro
 use core /* 0#1 */::prelude /* 0#1 */::rust_2018 /* 0#1 */::*;
 #[macro_use /* 0#1 */]
 extern crate core /* 0#1 */;
-extern crate compiler_builtins /* 444 */ as _ /* 0#1 */;
+extern crate compiler_builtins /* 445 */ as _ /* 0#1 */;
 // Don't load unnecessary hygiene information from std
 extern crate std /* 0#0 */;
 
diff --git a/tests/ui/proc-macro/nonterminal-token-hygiene.stdout b/tests/ui/proc-macro/nonterminal-token-hygiene.stdout
index 23a21004238..4031eb98a38 100644
--- a/tests/ui/proc-macro/nonterminal-token-hygiene.stdout
+++ b/tests/ui/proc-macro/nonterminal-token-hygiene.stdout
@@ -39,7 +39,7 @@ PRINT-BANG INPUT (DEBUG): TokenStream [
 use ::core /* 0#1 */::prelude /* 0#1 */::rust_2015 /* 0#1 */::*;
 #[macro_use /* 0#1 */]
 extern crate core /* 0#2 */;
-extern crate compiler_builtins /* 444 */ as _ /* 0#2 */;
+extern crate compiler_builtins /* 445 */ as _ /* 0#2 */;
 // Don't load unnecessary hygiene information from std
 extern crate std /* 0#0 */;